Alcohol process



Patented Jan. 31, 1959 ALCOHOL PROCESS Henry 0. Mottern, Hillside, N. J., assignor, by

mesne assignments, to Standard Oil Development Company, a corporation of Delaware No Drawing. Application December 14, 1945, Serial No. 635,107

11 Claims.

The present invention relates to an improved process for the production of aliphatic alcohols from olefinic hydrocarbons and more particularly to a process wherein the formation of polymer during the manufacture of secondary aliphatic alcohols can be materially reduced. The production of aliphatic monohydric alcohols through the absorption of olefinic hydrocarbons in mineral acids such as sulfuric acid using the cracked gases from a petroleum oil refinery as the source of aliphatic olefins. to form an acid extract which is subsequently hydrolyzed and distilled to recover the alcohol, is a widely used process.

Generally speaking, cracked gases are a heterogeneous mixture of saturated hydrocarbons, normal olefins, tertiary olefins, some hydrogen and small quantities or traces of other unsaturated hydrocarbons such as diolefins and acetylenes. For the purpose of this invention the tertiary olefins are best described as those monoor (ii-olefins which have in the molecule a carbon atom at the double bond attached to two other carbon atoms. Thus four valences of the tertiary carbon atom are occupied by three other carbon atoms. The first step toward economic utilization of cracked refinery gases is the separation of the gases into fractions, in which the hydrocarbons present have the samenumber of carbon atoms, by close fractionation. The next step in the refinery process is the separation of the various hydrocarbons within a particular fraction. This is accomplished by methods relying upon a marked difference in the reactivity of the various hydrocarbons. Of the major constituents present it is known that thetertiary olefins are the most reactive; next come the normal olefins; and the saturated hydrocarbons are inert under the described conditions of the extraction process. As for instance, isobutylene is removed from a mixture of isobutylene and normal butenes by reacting the mixture with a sulfuric acid of 62-65% acid strength on a hydrocarbon-free basis under conditions such that little if any of the normal butenes react, or the amylene fraction may be contacted with 65-75% sulfuric acid to remove the tertiary amylenes. However, the acid wash methed for separating tertiary olefins from normal olefins leaves small quantities of tertiary olefins behind with these normal olefins. In practice, the tertiary olefin present in such a fraction is usually 2-12% of the total hydrocarbon. When such fractions are contacted with mineral acid of sufilcient strength, e. g. 83-92% H2SO4, to react with the normal olefin to give an acid extract, large amounts of polymer are formed due to the polymerization of the tertiary olefins and copolymerization of the tertiary olefins and normal olefins.

The principal object of the present invention is to provide a process for producing alcohols from the normal olefins of cracked petroleum products which shall materially reduce the loss of olefins due to polymerization. This and other objects of the present invention will be apparent to. those skilled in the art upon reading the following description.

In the manufacture of secondary alcohols, as for instance secondary butyl alcohol, it is customary to contact a C4 cut containing -40% total olefin of which 2-12%, based on total hydrocarbon, is present as tertiary olefin or isobutylene, with a mineral acid, commonly sulfuric acid, in a multi-stage countercurrent system. It is in the first stage of a multi-stage countercurrent system where the extract contains the most absorbed olefin that the fresh olefin is fed, first coming in contact with acid extractant at this point. It is at this stage where at least one-half of the polymerization occurs. This polymerization involves not only the tertiary olefins present but also through copolymerization a considerable amount of the normal olefins contained in the original feed. Generally about 2 mols of normal olefin enter into the polymerization along with each mol of tertiary olefin; however, as much as 3 mols of normal olefin may enter into this reaction, and therefore, as much as 15-20% of the total olefin present in the original feed or even as much as 25% may be converted to polymer and 10st to alcohol production. Along with the polymer formation, the first stage absorbs a certain proportion of the olefin from the feed and each subsequent stage absorbs additional olefin until the effluent from the last stage contains less than 2% and generally only about .5% of olefin. The sulfuric acid esters formed by the absorption reaction are alkyl acid sulfate and dialkyl sulfate. The solubility of the dialkyl ester in the hydrocarbon phase depends to a degree more or less upon the concentration of the dialkyl ester in the acid phase, 1. e. a hydrocarbon phase in contact with an extract of high ester content will have dissolved therein a higher percentage of dialkyl ester than a hydrocarbon phase in contact with extract of low ester content. The relative olefinic content of an acid extract is expressed as a degree of saturation which is described by the molar ratio of olefin to acid present in the acid extract. I

It has now been found that by the addition of dialkyl ester and traces of free acid as found in a previously treated olefinic hydrocarbon mixture from a prior absorption process, to an olefin feed stock prior to contacting the olefin with acid in a multi-stage countercurrent system, the formation of polymers can be restricted to substantially that amount of polymer obtained by the polymerization of tertiary olefins only. The naphtha from any extraction stage may be used for recycling. Preferably the efiluent from either the first stage or the last stage of a countercurrent absorption system used in the process of producing alcohols from olefins may be used as the source from which to obtain dialkyl esters. The hydrocarbon from the last stage of the countercurrent system will be found to contain 6-8 grams of dialkyl ester per liter of hydrocarbon, the remainder being mostly saturated hydrocarbons". To recycle this hydrocarbon from the last stage to fresh olefin feed in any substantial amount would unnecessarily dilute the olefin feed. It therefore becomes necessary to concentrate the dialkyl ester in a portion of the hydrocarbon. This may be accomplished by a fractionator operated at a temperature above the boiling point of the lower molecular weght hydrocarbons present but below the temperature at which the dialkyl ester decomposes which removes the lower boiling fraction and the higher boiling fraction can then be blended into the fresh olefin feed. When operating in this manner traces of acid entrained in the spent hydrocarbon will also be carried into the untreated olefin.

Alternatively the dialkyl ester may be obtained by recycling the effluent from the first stage of the system to the fresh olefin feed. The ellluent from the first stage contains a much higher concentration of dialkyl ester than does the spent hydrocarbon from the last stage. This is because of the high concentration of dialkyl ester in the first stage" extract. The amount of dialkyl ester dissolved in the hydrocarbon phase in the first stage varies in accordance with the acid strength especially saturation of the extract on the basis of mols of olefin absorbed per mol of acid and may range from about 30 grams to about 150 grams or more of dialkyl ester per liter of hydrocarbon efiiuent. Since a large proportion of the original olefin feed remains in the hydrocarbon efiluent after a first stage of absorption, the hydrocarbon phase from the first stage can be recycled to the fresh olefin feed without unduly diluting the olefin. The amount of recycled hyd-rocarbon from the first stage to the olefin feed can be readily adjusted in accordance with the concentration of dialkyl ester present in the recycle stream and the tertiary olefin in the fresh feed. A surge drum or any other convenient means may be employed for pretreating the fresh olefin feed. After blending, the blend can be fed to the first stage in the countercurrent extraction system where it will be found that the amount of polymer formed will be 3-8% of the total olefin present in the olefin feed instead of the 15-25% formerly experienced.

The following examples are presented for the purpose of illustrating the invention.

Example 1 A C cut containing 98% total olefin and 14% tertiary amylene was continuously extracted with 83% sulfuric acid at 30 C. The volume propor tion of hydrocarbon to acid fed was 2-2.5:1. The

ill)

products were analyzed to determine the distribution of olefin with the following results:

Per cent olefin recovered as alcohol 55.5 Per cent olefin recovered, unchanged 22.9 Per cent olefin recovered as polymer 21.6

Percent of Percent 01 Percent of The Blend Olefin As Olefin As ggf lfg Polymer Alcohol changed,

05 Out+15% Recycle. 12.4 71.6 16 O5 Gut+25% Recycle. 9.0 74. 6 16.4 C5 Cut+4Q% Recycle... 7. 6 71. 8 20. 6 C5 Gut+% Recycle.-. 5.7 79.8 14. 5

Example 2 A dilute acid washed C4 cut containing 30.1% total olefin and 1.8% isobutylene was contacted With an already prepared extract of .855 mol of olefin per mol of sulfuric acid saturation made by absorbing C4 cut in 88% sulfuric acid at 30 C. The .855 saturated extract was contacted with the washed C4- cut at 30 C. and a volume ratio of 1 volume of extract to 10 volumes of C4 hydrocarbons. An analysis of the products showed the following olefin distribution.

Per cent of olefin recovered as polymer 12.3 Per cent of olefin recovered as alcohol 9.5 Per cent of olefin recovered unchanged 78.2

A blend of volume per cent of washed Ci cut identical with that described above with 50 volume per cent of a previously treated C4 cut was extracted with a .88 mol of olefin per mol of sulfuric acid saturated sulfuric acid extract at 30 C. The acid concentration of the sulfuric acid in the extract on an olefin-free basis was 88%. The extract of the blend was made under the same conditions and with the same proportion of reactants as above described. The treated naphtha contained 3.39 grams of dlbutyl sulfate per cc. of hydrocarbon and the blend had a total olefin content of 27.2%. An analysis of the products after extraction gave an olefin distribution as follows.

Per cent of olefin recovered as polymer ll 6 Per cent of olefin recovered as alcohol 16.9 Per cent of olefin recovered unchanged 77.1

Another sample of the 50 volume per cent blend was then extracted with fresh 88% sulfuric acid, having no olefin present, at 30 C., the other conditions and proportion of reactants remaining the same as that described in the next preceding experiment. An analysis of the products gave Per cent of olefin recovered as polymer 3.57 Per cent of olefin recovered as alcohol 56.43 Per cent of olefin recovered unchanged 40.0

What is claimed is:

1. In a process for producing secondary monohydrlc alcohols from aliphatic normal monoolefins which comprises contacting a hydrocarbon stream containing normal olefins and 244% tertiary olefins based on total hydrocarbon with a strong mineral acid in an absorption zone to form an acid extract phase of the normal olefin and a hydrocarbon phase containing dissolved dialkyl ester of the normal olefin and the mineral acid, which extract is subsequently hydrolyzed and secondary monohydric aliphatic alcohol recovered from the hydrolyzed extract, the improvement which comprises adding to the hydro carbon stream a hydrocarbon solution of the dialkyl ester of the normal olefin and the mineral acid containing traces of strong mineral acid prior to introduction of the hydrocarbon stream into the absorption zone.

2. A process according to claim 1 in which the hydrocarbon stream is contacted with sulfuric acid of 80-92 weight per cent concentration on a hydrocarbon free basis.

3. A process according to claim 1 in which the v hydrocarbon solution of dialkyl ester is added to the hydrocarbon stream in amounts of -50 volume per cent based on total hydrocarbon feed.

4. In a process for producing secondary butyl alcohol from normal butenes which comprises contacting a hydrocarbon stream containing normal butenes and 52-12% isobutylene based on total hydrocarbon with 80-92 Weight per cent sulfuric acid in an absorption zone to form an acid extract phase of the normal butenes and a hydrocarbon phase containing dissolved dibutyl sulfate, which extract is subsequently hydrolyzed and secondary butyl alcohol recovered from the hydrolyzed extract, the improvement which comprises adding to the hydrocarbon stream a hydrocarbon solution of dibutyl sulfate and traces of strong sulfuric acid prior to introduction of the hydrocarbon stream into the absorption zone.

5. A process according to claim 4 in which the hydrocarbon solution of dibutyl sulfate and traces of strong sulfuric acid are obtained from the hydrocarbon phase separated from the extract previously made in the process.

6. A process according to claim 4 in which the hydrocarbon solution of dibutyl sulfate and traces of strong sulfuric acid are added to the hydrocarbon stream in amounts of 440-50 volume per cent based on the total hydrocarbon stream.

7. In a process for producing secondary butyl alcohol from normal butenes which comprises contacting a hydrocarbon stream containing normal butenes and 2-12% isobutylene based on total hydrocarbon with 80-92 Weight per cent sulfuric acid in an absorption zone to form an acid extract phase of the normal butenes and a hydrocarbon phase containing dissolved dibutyl sulfate, which extract is subsequently hydrolyzed and secondary butyl alcohol recovered from the hydrolyzed extract, the improvement which comprises adding to the hydrocarbon stream a hydroall) carbon solution of dibutyl sulfate and traces of strong sulfuric acid prior to introduction of the hydrocarbon stream into the absorption zone.

8. In a process for producing secondary amylalcohol from normal pentenes which comprises contacting a hydrocarbon stream containing normal pentenes and 244% tertiary amylene based on total hydrocarbon with sulfuric acid of -92 weight per cent concentration in an absorption zone to form an acid extract phase of the normal pentenes and a hydrocarbon phase containing dissolved diamyl sulfate, which extract is subsequently hydrolyzed and secondary amyl alcohol recovered from the hydrolyzed extract, the improvement which comprises adding to the hydrocarbon stream a hydrocarbon solution of diamyl sulfate and traces of strong sulfuric acid prior to introduction of the hydrocarbon stream into the absorption zone.

9. In a process for producing secondary monohydric alcohols from aliphatic normal monoolefins which comprises contacting a hydrocarbon stream containing normal olefins and 214% tertiary olefins based on total hydrocarbon with a strong mineral acid in an absorption zone to form an acid extract phase containing the dialkyl ester of the normal olefin and the mineral acid, and a hydrocarbon phase also containing the dissolved dialkyl ester and traces of mineral acid, which extract is subsequently hydrolyzed and secondary monohydric alcohol recovered from the hydrolyzed extract, the improvement which comprises concentrating the dialkyl ester in the hydrocarbon phase by removal of a portion of the hydro carbons therein, and adding the concentrated hydrocarbon solution of dialkyl ester containing traces of mineral acid to the hydrocarbon stream.

prior to introduction of the hydrocarbon stream into the absorption zone.

10. A process according to claim 9 in which the secondary monohydric alcohol is secondary butyl alcohol, in which the strong mineral acid is sulfuric acid, and in which the dissolved dialkyl ester is dibutyl sulfate.

11. A process according to claim 9 in which the secondary monohydric alcohol is a secondary amyl alcohol, in which the strong mineral acid is sulfuric acid, and in which the dissolved dialkyl ester is diamyl sulfate.

HENRY O. MOTTERN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,938,177 Engs et al. Dec. 5, 1933 2,006,942 Clark July 2, 1935 2,042,212 Deanesly May 26, 1936 

1. IN A PROCESS FOR PRODUCING SECONDARY MONOHYDRIC ALCOHOLS FROM ALIPHATIC NORMAL MONOOLEFINS WHICH COMPRISES CONTACTING A HYDROCARBON STREAM CONTAINING NORMAL OLEFINS AND 2-14% TERTIARY OLEFINS BASED ON TOTAL HYDROCARBON WITH A STRONG MINERAL ACID IN AN ABSORPTION ZONE TO FORM AN ACID EXTRACT PHASE OF THE NORMAL OLEFIN AND A HYDROCARBON PHASE CONTAINING DISSOLVED DIALKYL ESTER OF THE NORMAL OLEFIN AND THE MINERAL ACID, WHICH EXTRACT IS SUBSEQUENTLY HYDROLYZED AND SECONDARY MONOHYDRIC ALIPHATIC ALCOHOL RECOVERED FROM THE HYDROLYZED EXTRACT, THE IMPROVEMENT WHICH COMPRISES ADDING TO THE HYDROCARBON STREAM A HYDROCARBON SOLUTION OF THE DIALKYL ESTER OF THE NORMAL OLEFIN AND THE MINERAL ACID CONTAINING TRACES OF STRONG MINERAL ACID PRIOR TO INTRODUCTION OF THE HYDROCARBON STREAM INTO THE ABSORPTION ZONE. 